Windshear is a phenomenon involving changing wind conditions in which wind velocity and direction may vary substantially over short distances or short time intervals. Windshears can result in hazardous flight conditions for aircraft during takeoff and on approach for landing. For example, a rapidly decreasing head wind may cause significant loss of lift which can be dangerous if the aircraft's airspeed is low or the aircraft's angle of attack is high as are both usually the case for an aircraft when landing. Further, the situation may be rendered more serious by the effects of sudden downdrafts which often accompany windshears and which diminish the climb capabilities of the aircraft. Therefore, it is highly desirable to develop accurate systems for detecting windshear and downdraft conditions so that the aircraft pilot can be warned to break off a land approach before the situation becomes critical.
Some systems of limited capability have been designed in the past to detect windshear. U.S. Pat. Nos. 4,012,713 and 4,079,905 to Greene describe a windshear detection system which uses airspeed, pitch attitude, and inertial acceleration signals to develop a windshear-type signal by differencing aerodynamically developed and inertially sensed accelerations. However, this system does not fully account for the effects of sensor dynamics, and does not distinguish between the true vertical and horizontal components of a windshear. Further, the system disclosed in the patents to Greene does not adjust the windshear signal for the effects of coriolis accelerations or for the effects of aircraft maneuvers.
U.S. Pat. No. 3,892,374 to Lambregts and U.S. Pat. No. 3,662,976 to Gesler also disclose systems which may be used for windshear detection in connection with throttle control devices. However, these systems are basic in design and include only the necessary components for differencing the deriviative of aircraft airspeed error with forward acceleration and, in the Lambregts case, certain filtering and rate limiting circuitry appropriate for the throttle control applications.
It is, therefore, an object of the present invention to provide a windshear detection system having greater accuracy, better reliability, and improved response time.
It is also an object of the present invention to provide such a system in which windshear signals are corrected for pitch rate induced coriolis accelerations to properly distinguish between vertical and horizontal windshear effects along the heading axis of the aircraft.
It is another object of the present invention to provide such a system that develops accurate input parameters and in which signals that are to be combined together are appropriately filtered to preserve their proper phase relationships.
It is a further object of the present invention to generate a loss of performance signal that is related to windshear and which includes the effects of vertical winds.